1. Field of the Invention
Embodiments of the invention described herein pertain to the field of floater-style centrifugal pump stages. More particularly, but not by way of limitation, one or more embodiments of the invention enable a thrust bearing surface for floater-style centrifugal pumps.
2. Description of the Related Art
Fluid, such as natural gas, water, oil or other hydrocarbons, is often located in underground formations. In such situations, the fluid is commonly pumped to the surface so that it can be collected, separated, refined, distributed and/or sold. Centrifugal pumps are typically used in submersible pump applications for lifting well fluid to the surface. Centrifugal pumps impart energy to a fluid by accelerating the fluid through a rotating impeller paired with a stationary diffuser. A rotating shaft runs through the central hub of the impeller and diffuser. A motor upstream of the pump turns the shaft of the pump motor. The shaft of the pump motor turns the pump shaft, and the impeller is keyed to the pump shaft, causing the impeller to rotate with the pump shaft.
Each rotating impeller and stationary diffuser pair is called a “stage”. The impeller's rotation confers angular momentum to the fluid passing through the pump. The angular momentum converts kinetic energy into pressure, thereby raising the pressure on the fluid and lifting it to the surface. Multiple stages of impeller and diffuser pairs may be used to further increase the pressure lift. The stages are stacked in series around the pump's shaft, with each successive impeller sitting on a diffuser of the previous stage.
As fluid moves upward through the pump, the rotating impellers exert a downward force as discharge pressure acts on the top of the impeller. The pump also experiences upward force from discharge pressure acting against the bottom of the impeller, and also due to the force produced by the momentum of the fluid making its turn in the impeller passageway. These axial forces are referred to as “thrust” experienced by the pump. Pumps capable of handling higher down thrust loads are able to operate at lower rates, which is beneficial due to extended operating ranges.
In both radial and mixed flow stages, one approach to handling the axial thrust of the pump is to allow each impeller to move axially on the pump shaft between the diffusers. In such instances, the impeller is keyed to the shaft within a key groove that runs axially along the length of the shaft. When the impellers can move independently of the shaft, the pump is referred to as a “floater style” pump.
To further improve a pump's thrust handling capabilities, thrust bearing surfaces consisting of a conventional nonrotating bushing and a conventional rotating flanged sleeve are typically inserted into pump stages. Together, the conventional bushing and conventional flanged sleeve form a conventional thrust bearing set. Typically, the conventional bushing is attached to the wall of the diffuser of the submersible pump and should not rotate. The sleeve is keyed to the shaft of the submersible pump and rotates with the shaft as fluid is pumped to the surface of a well. The conventional bushing is positioned concentrically around the conventional flanged sleeve, such that the conventional sleeve rotates within the bushing. As the pump operates, fluid is pulled between the bearing surfaces, increasing the pump's ability to handle thrust loads by providing hydrodynamic lift.
A conventional sleeve is illustrated in FIG. 1. As shown in FIG. 1, in conventional floater stages, conventional sleeve 100 includes a thin, disc-shaped conventional flange 105 at the top of the conventional sleeve. The flange is typically between 0.08 inches and 0.200 inches in thickness. The conventional flanged surface rotates inside the pump fluid, and also makes contact with a standoff sleeve. The standoff sleeve only makes contact with a narrow portion of the conventional flanged sleeve 100, closest to the shaft. The standoff sleeve supports the impeller. and the standoff sleeve length determines the operating height of the impeller. The standoff sleeve is typically Ni-resist austenitic cast iron alloy or stainless steel if shimmed.
Abrasives such as consolidated and unconsolidated sand, quartz or iron sulfide commonly mix with fluid pumped from downhole formations. As the fluid moves through the pump, the abrasives damage the pump components through erosive wear, and thrust bearings are no exception. Although thrust bearings are conventionally made of hard materials such as titanium carbide, tungsten carbide or silicon carbide, the thrust bearings are still susceptible to erosive wear from abrasives. Erosive wear to the thrust bearings causes them to leak, and the leakage reduces the hydrodynamic lift provided by the bearings and undesirably decreases head.
It would be an advantage for thrust bearings to have improved abrasive handling capability and improved resistance to leaks. Therefore, there is a need for improved thrust bearing surface for floater-style centrifugal pumps.